The process of bringing gases and solids into contact in materials handling procedures for various purposes including, but not limited to, drying, heating, cooling, granulating or conducting reactions are very common in many industries and it is typically beneficial to use additional solid particles to increase the solid material surface area. Such contactors may be packed beds, fluidized beds or spouting beds which differ primarily in the design of the inlets and distribution of the gas. The gas inlets may be smaller or larger than the additional solid particles. When the gas inlets are larger than the size of the solid particles the inlets can become clogged with solid material particles because the particles will flow back through the inlets when the gas supply is interrupted. When the gas supply is restored some or all of the inlets may remain plugged with solids. This then may require emptying the solids from the contactor, restarting the gas flow into an empty contactor and then adding the solids back in. Certain contactors, often termed spouted bed contactors, may have only one large inlet; such contactors are very beneficial for certain applications but are especially prone to plugging on gas flow interruption. Such contactors are becoming more popular for high temperature and high pressure operations such as coal or biomass gasification and the reaction of silicon tetrachloride and hydrogen with solid silicon.
Prior technology has primarily relied on preventing gas flow interruption or modifying the inlet size or structure. The most common approach is to prevent the particles from going into the inlets by making the inlets too small, by using self closing valves over the inlets, such as caps shown in Beranek U.S. Pat. No. 3,921,663, or balls as in Zhuber-Okrog U.S. Pat. No. 4,334,898. Another approach has been to restrict the distance the solids go when they flow backwards into the inlet by providing siphons as in Marcellini, U.S. Pat. No. 3,818,606. A yet further approach has been to allow the inlets to clog, then provide a separate unclogging gas flow as in Delebarre U.S. Pat. No. 4,880,311. Other techniques are to provide back up equipment to ensure that gas supply is not interrupted even for a brief period of time. For contactors with one or a few inlets it is possible to put solids valves on the inlets and close them rapidly if the gas flow is lost.
All the prior technologies involve significant cost and have known problems. Providing caps such as shown in Beranek and Zhuber-Okrog adds significantly to the cost and such devices are inherently prone to plugging in a solids environment because of particles jamming or otherwise interfering with the moving parts. Siphons as provided by Marcellini do not stop the backwards flow of solids because as the gas flow into the contactor is interrupted the solids and gas already in the contactor flows out of the contactor in a fluidized state and pass through the siphon. Thus a stop valve is required for each siphon as discussed in Delebarre. The approach provide by Delebarre provides a separate unclogging pipe to each orifice and valves to operate them and thus requires additional equipment and still relies on an elbow or siphon to stop the solids flow which does not work with fluidized solids. It is clear that Delebarre will also still require a stop valve as does Marcellini.
For a contacting device with a large single inlet that is typical of a spouted bed the gas flow needs to be vertical to generate the spout. Thus, cap devices are not useful because they direct the flow to the side as is seen in Beranek. Thus for such contactors significant costs are incurred by having equipment back up and an actuated solids valve close to the inlet and this valve can still fail to cut off the solids flow or may inadvertently activate when not needed. The timing of the opening and closing of the solids valve is particularly difficult. Also, as the valve is partly open there may be jetting of particles in the valve which can rapidly erode the seals of the valves. Closing the valve too fast or inadvertently will send potentially damaging pressure waves, also termed “water hammer”, back through the gas source system. Closing it too late or opening it too soon may plug the inlet, resulting in contactor shutdown and cleanup.